The present application claims benefit of Great Britain Application No. 9726620.9 filed Dec. 16, 1997.
The present invention relates generally to telecommunications systems, and more particularly to techniques for transmitting signalling information between a central terminal and a subscriber terminal of a telecommunications system.
In a typical telecommunications system, a subscriber terminal may be located at a subscriber""s premises for handling calls to and from that subscriber. One or more lines may be provided from the subscriber terminal for supporting one or more items of telecommunications equipment located at the subscriber""s premises. Further, a central terminal may be provided for controlling a number of subscriber terminals, and in particular for managing calls between a subscriber terminal and other components of a telecommunications network.
Typically, certain signalling information will be transmitted between the central terminal and the subscriber terminal to ensure that incoming and outgoing calls are handled correctly. To increase the efficiency of the telecommunications system, it is desirable to be able to minimise the amount of signalling information which needs to be passed between the central terminal and the subscriber terminal in order to perform the necessary signalling functions to establish and manage incoming and outgoing calls.
As the number of users of telecommunications networks increases, so there is an ever-increasing demand for such networks to be able to support more users. As techniques are developed to enable such systems to support more and more subscriber terminals, and hence more users, then it is clear that the bandwidth demands on the communication paths connecting the central terminal and the subscriber terminal are increased, this further increasing the need for efficient techniques for handling the signalling information which needs to be passed between the central terminal and the subscriber terminal to manage the calls.
It is hence an object of the present invention to provide a technique for efficiently handling signalling information passed between a central terminal and a subscriber terminal of a telecommunications system.
Viewed from a first aspect, the present invention provides a telecommunications system comprising an interface mechanism for passing signalling events between a central terminal and a subscriber terminal within the telecommunications system, the interface mechanism comprising: a signalling element within the central terminal for receiving a first signalling event for transmission to the subscriber terminal and for referencing a stored set of messages to determine a first signalling message to encode the first signalling event for transmission to the subscriber terminal; a signalling manager within the subscriber terminal for receiving the first signalling message from the central terminal, and for referencing said stored set of messages to decode the first signalling message to determine the first signalling event; the signalling manager being arranged to receive a second signalling event for transmission to the central terminal and for encoding the second signalling event as a predetermined signalling message from said stored set of messages, a parameter of the predetermined signalling message being arranged to contain information identifying the type of the second signalling event.
In accordance with the present invention, a core set of messages can be defined to represent all of the necessary signalling events which may need to be communicated between the central terminal and the subscriber terminal. By defining a core set of messages, the number of bits required to define each message is relatively small, this assisting in reducing the bandwidth demands required for signalling.
Further, it has been found that there are generally more bandwidth restrictions on the uplink communication from the subscriber terminal to the central terminal, since lower duplex rates are often employed on the uplink communication than are employed on the downlink communication. To alleviate this problem, in accordance with the present invention, a predetermined signalling message is defined which can be used to encode a plurality of different signalling events which may need to be transferred from the subscriber terminal to the central terminal, a parameter of the predetermined signalling message being arranged to contain information identifying the signalling event type. By using a predetermined signalling message rather than a number of separate signalling messages, the signalling message can be defined using less bits, thereby further reducing the bandwidth required on the uplink communication for signalling purposes. This is useful, since in preferred embodiments, there is often more signalling information being transmitted on the uplink than on the downlink communication path, and so the reduction in bandwidth obtained from using the predetermined signalling message helps to alleviate the extra bandwidth demands resulting from the uplink signalling information.
In preferred embodiments, the predetermined signalling message used to encode the second signalling event has a plurality of parameter fields, and the signalling manager is arranged to use the plurality of parameter fields to represent a plurality of said second signalling events within the predetermined signalling message.
By this approach, further bandwidth savings can be achieved, since it is not necessary to issue the predetermined signalling message for each item of signalling information. Instead, multiple items of signalling information can be received by the signalling manager, and the signalling manager can then be arranged to package those multiple items of signalling information within one predetermined signalling message, thereby making efficient use of the available bandwidth to further reduce the bandwidth required for signalling purposes.
It will be appreciated that the signalling element within the central terminal may take a number of different forms. However, in preferred embodiments, the signalling element comprises: a signalling port arranged to receive the first signalling event, and with reference to the stored set of messages, to generate the first signalling message; and a signalling multiplexer arranged to cause the first signalling message to be transmitted to the subscriber terminal.
In preferred embodiments, a plurality of subscriber terminals are associated with the central terminal, each subscriber terminal being arranged to provide one or more telecommunications lines for connecting items of telecommunications equipment to the subscriber terminal, the central terminal includes a signalling multiplexer for each subscriber terminal associated with the central terminal, and each signalling multiplexer has associated therewith a signalling port for each telecommunications line that can be supported by the corresponding subscriber terminal.
Hence, in preferred embodiments, signalling events pertaining to a particular telecommunications line of a particular subscriber terminal will be handled by a particular signalling port associated with the signalling multiplexer provided for that subscriber terminal.
Preferably, for an incoming call to a particular telecommunications line of a subscriber terminal, the corresponding signalling port is arranged to receive a setup signalling event, and to generate a setup message including as a parameter an identifier of the telecommunications line to which the incoming call is directed, the signalling manager being arranged to decode the setup message to determine the setup signalling event, and to have the setup signalling event processed within the subscriber terminal to cause the telecommunications equipment connected to the particular telecommunications line to generate an incoming call indication.
The incoming call indication can take any appropriate form, and will typically depend on the type of telecommunications equipment connected to the telecommunications line. If the telecommunications equipment is a telephone, then the incoming call indication will typically involve turning the telephone ringer on. In preferred embodiments, further signalling messages can be sent from the central terminal to the subscriber terminal to control the duration of each ring of the telephone.
In preferred embodiments, when an incoming call is accepted at the subscriber terminal, an off-hook signalling event indicating that the incoming call is connected is generated, and the signalling manager is responsive to that off-hook signalling event to produce the predetermined signalling message with a parameter of the predetermined signalling message identifying that the incoming call is connected.
Typically, the off-hook signalling event will be generated by the subscriber terminal in response to the connected item of telecommunications equipment receiving the incoming call, such as for example when a user picks up the handset of a telephone.
The number of items for telecommunications equipment supported by a single subscriber terminal can vary, depending on a number of factors, such as the available bandwidth for connections between the central terminal and the subscriber terminal. However, in preferred embodiments, one or more telecommunications lines are provided by the subscriber terminal for connecting items of telecommunications equipment to the subscriber terminal, a signalling processor is provided within the subscriber terminal for each telecommunications line supported by the subscriber terminal, and the signalling manager is arranged to determine from a parameter of the first signalling message the telecommunications line to which the first signalling event is directed, and to forward the decoded first signalling event to the corresponding signalling processor.
Preferably, the parameter of the first signalling message used by the signalling manager to determine the telecommunications line to which the first signalling event is directed is a line number identifying the telecommunications line to which the first signalling event is directed.
For an outgoing call from the subscriber terminal, the signalling manager is preferably arranged to generate the predetermined signalling message with a parameter of the predetermined signalling message indicating a setup signalling event, the signalling element being arranged to decode the predetermined signalling message with reference to said stored set of messages to generate a signalling event for processing by the central terminal.
Further, when the outgoing call is accepted at the central terminal, then in preferred embodiments a setup confirm signalling event indicating that the outgoing call is connected is received by the signalling element, and the signalling element is responsive to said setup confirm signalling event to produce a connect message to represent the setup confirm signalling event, the signalling manager being arranged to decode the connect message to produce a signalling event confirming that the outgoing call is connected.
During the operation of the telecommunications system, it is often necessary to periodically test certain elements within the telecommunications system, and these test procedures also often require the transmission of test information between the central terminal and the subscriber terminal. As with signalling information, it is desirable to minimise the amount of test information that needs to be passed between the central terminal and the subscriber terminal in order to perform these required test routines.
Hence, in preferred embodiments, the signalling element is further arranged to receive a first test event for transmission to the subscriber terminal and is arranged to reference the stored set of messages to determine a first test message to encode the first test event for transmission to the subscriber terminal.
Further, the signalling manager within the subscriber terminal is preferably arranged to receive the first test message and to reference said stored set of messages to decode the first test message to determine the first test event.
Additionally, in preferred embodiments, the signalling manager may be arranged to receive a second test event for transmission to the central terminal and to encode the second test event as a predetermined test message from said stored set of messages, a parameter of the predetermined test message being arranged to contain information identifying the type of the second test event.
In accordance with the above preferred embodiment of the present invention, the core set of messages is defined to represent not only all of the necessary signalling events which may need to be communicated between the central terminal and the subscriber terminal, but also the necessary test events. By defining a core set of messages, the number of bits required to define each message is relatively small, this assisting in reducing the bandwidth demands required for testing.
In preferred embodiments, the predetermined test message used to encode the second test event has a plurality of parameter fields, and the signalling manager is arranged to use the plurality of parameter fields to represent a plurality of said second test events within the predetermined test message. By this approach, further bandwidth savings can be realised since it is not necessary to issue the predetermined test message for each item of test information.
Preferably, the telecommunications system further comprises a test processor within the subscriber terminal to which the signalling manager is arranged to pass the first test event for processing by the test processor. In preferred embodiments, one test processor is provided per subscriber terminal, although more than one test processor could be provided if desired.
The present invention may be employed in any type of telecommunications system, for example a wired telecommunications system, or a wireless telecommunications system. However, in preferred embodiments, the central terminal and subscriber terminal are connected by a wireless link, and the central terminal and subscriber terminal comprise link connection mechanisms for establishing the wireless link for incoming and outgoing calls.
Viewed from a second aspect, the present invention provides a central terminal for a telecommunications system in accordance with the first aspect of the present invention, the central terminal comprising a signalling element for receiving a first signalling event for transmission to a subscriber terminal and for referencing a stored set of messages to determine a first signalling message to encode the first signalling event for transmission to the subscriber terminal, the signalling element further being arranged to decode, with reference to the stored set of messages, signalling messages received from the subscriber terminal in order to generate signalling events for processing by the central terminal.
Viewed from a third aspect, the present invention provides a subscriber terminal for a telecommunications system in accordance with the first aspect of the present invention, the subscriber terminal comprising a signalling manager for receiving a first signalling message from a central terminal, and for referencing a stored set of messages to decode the first signalling message to determine a first signalling event for processing by the subscriber terminal; the signalling manager further being arranged to receive a second signalling event for transmission to the central terminal and for encoding the second signalling event as a predetermined signalling message from said stored set of messages, a parameter of the predetermined signalling message being arranged to contain information identifying the signalling event type.
Viewed from a fourth aspect, the present invention provides a method of handling signalling events passed between a central terminal and a subscriber terminal of a telecommunications system, the method comprising the steps of: arranging a signalling element within the central terminal to be responsive to receipt of a first signalling event for transmission to the subscriber terminal to reference a stored set of messages to determine a first signalling message; encoding the first signalling event as said first signalling message; transmitting the first signalling message to the subscriber terminal; arranging a signalling manager within the subscriber terminal to receive the first signalling message from the central terminal, and, with reference to said stored set of messages, to decode the first signalling message to determine the first signalling event; receiving at the signalling manager a second signalling event for transmission to the central terminal; encoding the second signalling event as a predetermined signalling message from said stored set of messages, and providing as a parameter of the predetermined signalling message information identifying the type of the second signalling event.